Data storage systems use magnetic media for storage of digital information. For example, disc drives use rigid or flexible discs coated with a magnetizable medium for storing information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g., air) bearing disc head sliders. The sliders carry transducers, which write information to and read information from the disc surface. An actuator mechanism moves the sliders from track to track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each slider. The suspension includes a load beam and a gimbal. The load beam provides a load force, which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam, or is integrated in the load beam, to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
The slider includes a slider body having a bearing surface, such as an air bearing surface, which faces the disc surface. As the disc rotates, the air pressure between the disc and the air bearing surface increases and creates a hydrodynamic lifting force, which causes the slider to lift and fly above the disc surface. The preload force supplied by the load beam counteracts the hydrodynamic lifting force. The preload force and the hydrodynamic lifting force reach an equilibrium, which determines the flying height of the transducer relative to the disc surface. The transducer is typically mounted at or near the trailing edge of the slider. The geometry of the bearing surface effects the flying characteristics of the slider, such as the dynamic pitch and roll attitude of the slider.
In some applications, the slider flies in close proximity to the surface of the disc. This type of slider is known as a “pseudo-contact” slider, since the bearing surface of the slider can occasionally contact the surface roughness of the disc. In other applications, the slider is designed to remain in direct contact with the disc surface with substantially no air bearing. These sliders are referred to as “contact recording” sliders.
It is often desirable to fabricate a slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as cross or camber curvature. The proper setting and control of crown and cross curvature improves flying height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface. Therefore, there is a need for a method of controlling the slider curvature and for a method of accurately characterizing the surface shape so that the curvature control is accurate and the resulting performance of the slider can be predicted.
A traditional method of creating crown or cross curvature is to lap the bearing surface on a spherically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of the desired curvature. The amount of curvature is determined by the radius of the rocking rotation. This lapping process is difficult to control and results in large manufacturing tolerances. Therefore, more efficient and controllable methods of effecting air bearing surface curvature are being developed.
U.S. Pat. No. 5,442,850 discloses a method of controlling curvature by inducing a preselected amount of compressive stress within the bearing surface by impinging the bearing surface with particles for a preselected amount of time. U.S. Pat. No. 5,266,769 discloses a process of controlling slider curvature in which the air bearing surfaces are first patterned and then a chosen pattern of stress is produced on the back side of the slider by laser oblation or sand blasting to selectively remove stressed material and thereby create a desired crown and cross curvature of the bearing surface.
U.S. Pat. No. 5,982,583 discloses a method of effecting slider curvature through the application of laser-induced anisotropic tensile stress, which allows one of the crown and cross curvature to be changed to a greater extent than the other curvature. The use of laser scribe lines to adjust curvature are also disclosed in U.S. Pat. Nos. 6,108,170, 6,321,440, 6,548,009, 6,531,084, and 6,441,385, for example.
While the above methods improve curvature control, additional control is desired. Traditional methods of curvature control view crown and cross curvature as global metrics of the slider as a whole, not within localized areas within the slider. Also, traditional methods attempted to control some of the shape parameters of the slider while ignoring that changes aimed at controlling any given shape parameter may impact other important slider parameters. Improved methods of controlling the shape parameters are therefore desired.
Similarly, traditional methods of characterizing the slider shape, either prior to or after curvature control methods have been applied, describe the global curvature of the slider. For example, the slider has been characterized by global crown, cross and twist curvature values. These methods have not captured the finer details of the slider shape, thereby making curvature control methods and performance models less accurate.
For example in one prior art method, the global crown, cross and twist curvature values are derived from a second-order polynomial fit to data representing measured heights at a plurality of locations on the air bearing surface. The curvature of the slider is measured at discrete points (xi, yi) and a least-square fit is performed to minimize the error between measured data (zi) and a quadratic polynomial:Σ[zi−(a+bxi+cyi+dxi2+exiyi+fyi2)]2=min  EQ. 1where zi is the measured height of the air bearing surface at location “i”, xi represents a location along a longitudinal “x” axis of the slider, yi represents a location along a transverse “y” axis of the slider, and the coefficients a, b, c, d, e, and f are the results of the least-square fit. Once the coefficients a, b, c, d, e and f are determined, the crown, cross and twist are given by:
                                                        crown              =                            ⁢                                                                    -                    d                                    *                                      sliderlength                    2                                                  4                                                                                        camber              =                            ⁢                                                                    -                    f                                    *                                      sliderwidth                    2                                                  4                                                                                        twist              =                            ⁢                                                -                  e                                *                sliderlength                *                sliderwidth                                                                        EQ        .                                  ⁢        2            
These three parameters describe the global curvature of the slider, not the details of the slider shape. Improved shape characterization techniques are desired, which solve this problem and enhance measurement and modeling capabilities.